Scrub the mussels and discard any that do not close when tapped.
Fill a steamer or wok with 5cm of water and bring to a boil.
Place the mussels on a plate inside the steamer or on the rack.
Reduce heat to low and cover the vessel tightly.
Steam gently for five minutes until the mussels begin to open.
Combine all sauce ingredients except the oil in a heatproof bowl.
Heat oil in a wok until smoking and pour it over the sauce ingredients.
Remove mussels from the steamer and discard any that remain closed.
Stir the sauce and pour it over the opened mussels.
Garnish with fresh coriander and serve immediately.